Various methods for the synthesis of diaromatic alkylphosphonates are known. Methods for making diaromatic alkylphosphonates are described in U.S. Pat. Nos. 4,152,373 and 4,377,537, for example. In U.S. Pat. No. 4,152,373, diaromatic alkylphosphonates are prepared by the reaction of a triaromaticphosphite specifically triphenylphosphite and methanol in the presence of a catalytic amount of methyl iodide. The reaction temperatures are higher than the boiling point of methanol (˜65° C.), and consequently require a relatively slow addition of methanol in order to keep it from boiling out of the reactor. In this reaction, phenol is a by-product that is distilled from the product in a separate step.
U.S. Pat. No. 4,377,537 describes a method of synthesizing diaromatic methylphosphonates by the reaction of a triarylphosphite (specifically triphenylphosphite) and trialkylphosphite (specifically trimethylphosphite) in the process of a catalytic amount of methyl iodide. The reaction typically involves heating the components to a final temperature of about 230° C. for up to 1 hour. Exothermic reactions for this process occur in two temperature regions, the first around 100° C., and the second near 210° C. Due to the exothermic (even explosive) nature of these reactions when used in a batch process, the reaction scheme described in U.S. Pat. No. 4,377,537 is limited to small scale production of diaromatic alkylphosphonates.
Although some diaromatic alkylphosphonates (e.g. diphenyl methylphosphonate) (Registry number 7526-26-3) are commercially available, they are relatively expensive.